Against a plucky Leicester side at a packed and tense Emirates Stadium, Arsene Wenger's men scored twice in the last 10 minutes - first through substitute Aaron Ramsey before the much-maligned Giroud headed in the victor off Granit Xhaka's corner.
With time running out, Arsenal needed some sort of miracle, and they got just that from Aaron Ramsey and Olivier Giroud.
Following his new two-year contract the pressure had eased on Wenger over the summer after improved displays in April and May with a 3-4-3 system, an FA Cup victory to end last season and the signing of Alexandre Lacazette.
For Arsenal, some positive momentum had already been achieved after beating Chelsea to win the Community Shield, and it continued early Friday, as Lacazette announced his arrival immediately with an unmarked yet hard and instinctive header off Mohamed Elneny's chipped-forward assist to give Arsenal a 1-0 lead.
This was only the sixth time that an opening game in a Premier League season has seen seven goals scored- no game has seen more.
Left backs Nacho Monreal and Sead Kolasinac manned the middle of the defense, Giroud scored and the Gunners came from behind.
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Guardiola, a former Barcelona and Bayern Munich manager , has yet to win a trophy since taking charge of City at the start of last season.
'A player I am a big fan of, ' is how Jamie Carragher described Olivier Giroud on Friday night. "We love him and in the end he chose to stay". Arsenal were twice behind against Craig Shakespeare's side.
"Starting games is a different thing altogether, but he will score goals".
Schmeichel thwarted Oxlade-Chamberlain and Bellerin before Wenger turned to his bench in the 67th minute, pitching Ramsey and Giroud into the fray in place of Elneny and Rob Holding.
The Frenchman wants to see the Gunners' record signing Alexandre Lacazette emulate what the 35-year-old former Sweden worldwide striker did in the Premier League.
Two goals in the first 10 minutes and two in the last 10 - if that doesn't rekindle the excitement of Premier League football, not much can. We have a game backed on mobility and technique and I think he can integrate that well.
After the victory, the Arsenal boss was quick to praise his team and the impact Lacazette made on his Premier League debut. The Gunners' defending was suspect, but Vardy did well to get in front of them and to put his chance away, restoring the Foxes' lead.